Mobile power supplies are widely used because they can conveniently charge devices such as tablet computers and mobile phones. As shown in FIG. 1, a mobile power supply 1 includes a large-capacity battery 10, a power supply management circuit 11, an inbound charging interface 12, an outbound charging interface 13, and the like. The inbound charging interface 12 is used by an external battery charger to charge the mobile power supply 1. The outbound charging interface 13 is used by the mobile power supply 1 to charge an external device (such as a tablet computer or a mobile phone). The mobile power supply 1 preferably can perform inbound charging and outbound charging at the same time, so that a user can conveniently use the mobile power supply 1.
As shown in FIG. 1, some users may directly connect the inbound charging interface 12 to the outbound charging interface 13. As a result, a current loop (the current loop is referred to as a self-loop below) is formed in the mobile power supply 1. Consequently, electric energy of the mobile power supply 1 is consumed in vain. In addition, if the inbound charging interface 12 and the outbound charging interface 13 are connected for an excessively long time, excessive heat of the mobile power supply 1 may even damage an internal circuit of the mobile power supply 1. Currently, it is not detected whether a self-loop exists in the mobile power supply 1 when the mobile power supply 1 performs inbound charging and outbound charging at the same time.